1. Field of the Invention
The invention relates to liquid, band pass filters and more particularly relates to the use of 2,7-dimethyldiaza-(3,6)-cycloheptadien-(1,6)-perchlorate solutions as such optical filters.
2. Brief Description of the Prior Art
The compound 2,7-dimethyl-diaza-(3,6)-cycloheptadien-(1,6)-perchlorate (sometimes referred to in the art as "Cation X") has been used prior to my invention as a component of the well known "Barr filter". The Barr filter is a solid type of band pass filter which comprises a suspension of the "Cation X" in a thin film of polyvinyl alcohol.
The prior art Barr filters are not satisfactory for all purposes as ultraviolet transmission filters since random variations in the polyvinyl alcohol film thickness prevents one from obtaining a controlled concentration of the suspended Cation X over a given surface area. Further, the polyvinyl alcohol component of the filter may produce undesirable absorption of light waves in certain pass bands of interest.
I have found that the above-described problems of the Barr filters are avoided by the use of the Cation X in solution, preferably a glycerol solution.
The corresponding 2,7-dimethyl-diaza-(3,6)-cycloheptadien-(1,6)-iodide has been employed in an aqueous solution as a liquid band pass filter; see Kasha, JOSA, 38 No. 11, page 929 (November 1948).